A type of known fuel injection system for an internal combustion engine comprises a high pressure pump, a common rail and a plurality of fuel injectors, each of which is associated with a respective combustion chamber of the engine.
The high pressure pump is arranged to receive fuel at low pressure from a fuel supply, such as a vehicle fuel tank, and to pump fuel at high pressure, e.g. 2000 bar, into the common rail. The common rail feeds each of the plurality of fuel injectors with fuel at high pressure.
It is known to control the delivery of fuel at a high pressure to the common rail by means of an electro-valve (Flow metering valve) situated on the pump low pressure side. A second electro-valve situated at one end of the High pressure common rail serves to discharge the common rail when a rapid deceleration of the engine occurs or when the pressure in the rail exceeds the system pressure demand, while maintaining a minimum pressure, or to discharge the common rail when the engine is at stop and to help heating the fuel for a cold start.
Such known device comprises a valve comprising a ball carried by a movable longitudinal axis at one end, the other end of said movable axis being attached to a movable plunger actuated by an electro-magnetic coil, said movable plunger being placed, at least partially, inside a magnetic bearing cap.
A large clearance is arranged between the movable plunger and the surrounding magnetic cap, said clearance being filled with fuel, in order to lubricate the displacements of the movable plunger inside the cap.
However, in reality the large fuel gap between plunger and cap leads to uncontrolled dynamic motion of plunger and loss of magnetic force. Without damping, there are instabilities in pressure control, back leak pressure spikes and associated noise of the system.
An object of the present invention is to suppress such drawbacks.